-sigh- -leans forehead on hand-

Compression height of the piston has ABSOLUTELY NOTHING to do with hp / torque. ROD LENGTH compared to STROKE, also known as ROD RATIO, does, to some extent. In a 360 with 6.488" rods, the piston velocity is going to be nice and slow anyway. It's not anything like the 351m that wedges it up there and quick sucks it back down the bore. The 360 will let it set there for a while. (so will a 390 to a certain extent, but that's not what we're talking about right now)

DD2k shows it'll make PLENTY of HP with the appropriate heads / cam. Heads and cam are where hp is made. Period. Anyone that says piston compression height alone has anything more than a negligable affect on horsepower is blowing smoke.

About .060" is the maximum clearance between the head and piston to still have quench be effective. Ideal, I believe, is between .020" and .060". So at .040" you're about perfect. You wont carbon it up that quick. Maybe if you drove like a grandma for 3 years in a row, maybe. But rev it up every now and then and it will be fine.

You want the proper quench distance because what happens, is the fuel / air mixture is forced out from between the piston top and head, into the open part of the combustion chamber, at high speed. This accomplishes two things, it cools off hot spots by blowing more air / fuel past them, and it prevents the fuel / air from becoming stagnant in any particular area and heating up more and preigniting. This is known as turbulence. It reduces an engines tendency to ping A LOT. So, zero deck, in this case, is desirable.

There is a drawback to pistons with a higher compression height though. That is piston weight. The more a piston weighs, the more stress it puts on the rod. When having them balance the engine, have them remove as much weight as safely possible from the pistons before adding to the crank to balance things out. However, in an engine like a 360, with comparitavely long rods, compared to other Ford engines, the piston velocity is nice and low. Slow to accelerate and decelerate. So piston weight is not nearly as much an issue with FE's as it is with, say a 347 stroker.

Hope this clears up some things.

 

If the piston height has nothing to do with how fast it revs, then why did every 400 I ever drove run SO much better than the 351M ? I had a 77 351M and it was a DOG, and ditto for every other one that anybody I talked to said about them. The only difference between the two was the stoke and the pistons. And on top of that every 351W and Cleveland I drove rev'd just fine. Only difference there was the shorter rods and pistons. Even the ones I drove from the mid 70's( 351W & C) . Taller pistons DO have an effect on how it revs, they add unnecessary weight to the rotating assembly for one. also increased friction from their longer skirts. If he wants to waste his money on custom pistons when swapping in a much cheaper 390 crank would be more cost effective, then it's his money. But that extra money could be better spent on power producing parts that REALLY make a difference instead of custom pistons that do nothing for performance. For instance the money he saves could be used to buy a set of full roller rockers and new shafts and stands to go with them, which for what they cost is about equal to what he'll spend extra over a set of off the shelf 390 flattop pistons. But hell, what do I know, go ahead and spend the $500 on custom pistons, you'll sure be disappointed when some yahoo with the same combo you have but with a 390 under the hood walks off and leaves you.

 

Hrm, lets see here. The '77 351m was a severely detuned smog motor. Big time. So was the 400. Well, the extra cubic inches helped there. IT WAS NOT THE PISTONS!

Of course the Cleveland revs fine, not a detuned smog motor and plenty of head flow per cubic inch.

So he should just forget about it and build a 390? Why not just tell everyone to build a chebby 350? Where's the individuality?

Ok, so we're going with the path of least resistance. I can do that. Buy a GM performance parts Deluxe 350 crate engine for $3495 from Jegs, and a TH700R4 from Jegs for $1463. Project complete.

 

Nobody mentioned the "C" word but you. And yes, I have driven a 74 Cleveland, and yes they were just as detuned as the year later 351M, but they were still a much better performer than the M. And apparently I didn't get the point across on building a 390 instead and using the money saved on custom pistons, on better parts to increase HP production . What part of that didn't you understand ? Hell instead of custom pistons, He could just use Silvolite's replacements for the 361 FT engine and add a blower to increase the 7.0 to 1 ratio they give. And after that, it would STILL get beat by a 390.

 

It's great to read throught the debate. I love building engines. I have built plenty of SBC, but since my interests have moved to mostly to Ford's I am really in a learning mode myself. I know a little about the 360's since I have had a few of those...I had a 406 for a short time, but that is about it with FE blocks. So, I want to do something with my 360. I have learned here that the compression is low on these engines and that I need more compression for more ponies. In this discussion, it appears pistion selection and deck clearance are very important. I have a set of C8AE-H heads, which can be valved up to 2.08 and 1.66 for better performance and that flat top pistons with zero deck is best. I am assuming the C8AE-H are around 70cc or so. I guess I would have to pull them to know for sure since Ford shows these as 68cc to 71.1cc for this casting. Anyway, with new pistions and crank I can go to 390 internally balanced or the 410 externally balanced. So, I still need to learn about externally balanced parts...whats need and if this is smart idea or just stick with the 390. All I really want is something sporty to pull around my 4,750 lbs LB F-100. (375 HP maybe 400 HP) Something FUN! I like the FE's though...sure I could just install an 400HP DOC 32V Intech 4.6...but that does not sound like any fun. Thanks for the help guys!!

 

Well if you're going to take the easy way out, why not go all the way? Thus, the C word. That's what you didn't get across. Egoman knows it would be easier to build a 390. He asked for help with 360 pistons. I provided that. What the **** is wrong with that?

And blowers cost $500? What world are you living in? Besides, the cast 361FT replacement pistons would never hold up under boost for very long.

And no, I could build a 360 that would blow the doors off a 390. All it takes is more flow through the heads. Same cam, same compression. There's nothing magical about a 390. The only advantage is you can get off the shelf pistons for it.

Just ask, I'll post my suggested 360 build and DD2k numbers.

OBTW, if piston compression height is so overwhelmingly important in HP production, why do most of the major engine simulation programs not have a selection for compression height, rod ratio, or piston weight?

 

The main problem that started the debate was Egoman's wanting to use 390 rods in a 360. It won't work without custom pistons. And as I said before using taller custom pistons is both expensive and adds nothing to the performance, when using a cheaper 390 crank is a better solution. As for what you want to do a 390 is the most cost effective route. It's very simple and cheap to get 375-400 hp with a 390, nothing tricky about it. Going the 410 route adds very little torque for a whole lot of extra money, both in purchasing a 410/428 crank and adding balancing. Balancing doesn't have to be external, any competant engine balance shop can balance one internally. I had this done on a stroked 427 lowriser for no other reason than to use easy to acquire 390 flywheels. Your C8AE-H heads will get you there even with stock sized valves. All that's needed is a basic rebuild to get a 10.5 to 1 comp ratio ( if your's doesn't already have the 4 bbl car pistons), a relatively mild cam, something with around a .500-550 lift and a 290 degree ( advertised) duration, either a Performer RPM or a Ford 427MR/428PI intake, a 750 carb, headers, and a little cleanup and port work on the heads.

 

You can quote DD2k numbers till the cows come home, I don't deal with them, real #'s only, and maybe, because they don't add those specs into the equation, that could be the reason real engines don't produce the DD2k numbers in real life. And yes, piston comp height has everything to do with HP production, apparently if you think they don't then you have a lot to learn. If he wants a 360 and the easy route then he needs to just stick with 360 rods and pistons and hope they hold up.

 

360 rods?? That's the dumbest thing I've heard yet! Those suckers would snap like toothpicks above 6000rpm. 5000 to 6000rpm would stress them and they might last a few runs, then snap. And still, he'd need custom pistons.

I'll say it one last time. The affect of a taller piston will be negligable. 10 hp or less. They will change the compression ratio however, and THAT changes performance.

If DD is so inacurate, why was an engine built on a popular TV show, Hot Rod I think, and it came out to within 3hp of the predicted figure?

Ok, if he's set on building a 360, how about this. Have a custom crank ground for 6.7" BBC rods. That'd solve the compression height "problems" eh?

I can see that I'm not going to convince you that you're wrong. Oh well. Some people you just cant reach.

 

Well I'm doing two niulds I got the 416 motor which is going to cost about 7k give or take.....And the 360 idea. The 360 motor should only cost about 3 grand not counting the erson roller rockers. I just figured it would be a great build for a street truck kinda mild yet with some *****. I can see the weight issue but I think that balancing can help in that area. Other than that the only differance between that and the 390 is the torque from the crank. I dont honestly think ill miss it that much plus I like to take long drives at high speed, nothing beats dropping a gear and passing on the freeway.....well accept hauling *** down the track I just want to know If there is a serios issue that could arise with the tall piston? I wouldnt think so considering that it was used in a production vehicle to begin with. hell i think the 941 cam will accept an 8.75:1 compression ratio...I bet that with heads and intake and a 901 cam it would be worlds of differance in the performance just with the stock 360 setup(rods crank and piston height). what do ya'll think?

 

Well...nice thought there rusty! the BBC rods I never thought of that lol!

 

Finally some sense in here. If you want to just build a simple 360 for your truck, then yes, a 901 cam will wake it up good. The 941 may be a little big. There again, you need to up the compression ratio.

An idea just popped into my head. If taller pistons are so absurdly horrible (which I still dont think they are, except at the track to gain that last 10th) then why not a standard compression height piston with a small dome?

 

I probably should have started a new post here...it seems that I am off topic in regard to the orginal question. Piston use on the 360 was interesting and one thing lead to another...sorry about that.

 

Wouldnt that still be a custom piston though? If i could get 9.0:1 I could run the 941 cam. But with a 410 piston and a bbc rod I could get just over 9:1 and it will cost about the same. The onlt differance in the 360 to the 390 is a couple of foot pouns of tourqe and thats not going to blow any doors off.....I could make that up in weight.

 

Well, when you use a BBC rod, your piston selection changes somewhat I believe. The BBC rod uses a wrist pin diameter of .9898", while the FE uses a pin diameter of .9752" Not a whole lot of difference, but enough to screw things up. Plus, the BBC bore diameter is different. Whether or not you can modify an existing FE piston to use the larger pin remains to be seen, however, there again you're adding cost to the build, both for modifying the piston and for custom pins.

I'll see what I can find, I'll let you know in the morning. However, it looks like the easy solution is 390.

You just cant win.